1. Field of the Invention
This invention relates to the recovery of liquid hydrocarbons (oil, gasoline and other petroleum products) which may be found underground floating on top of the water table or may be floating as a thin layer on the surface of lagoons and ponds. The liquid hydrocarbons are generally present in these locations, particularly floating on ground water, because of an unintentional oil spill or leakage from a storage tank or other facility.
2. Description of the Related Art
It is well known that the numerous and widely distributed. facilities for the handling of oil and petroleum products, such as service stations, terminals, refineries, pipe lines, etc., inevitably produce (indeed, have produced on many occasions) accidental spills and leaks such that substantial quantities of liquid hydrocarbons are lost into the subsurface soil. In most cases, this liquid filters through the soil and finally accumulates on the water table where it remains as a contamination which must be removed. Equipment and methods used in handling surface spills are generally of no use in cleaning up subsurface contamination because of the greatly different parameters of the recovery problems which are involved.
One common method of underground liquid hydrocarbon recovery is to drill a well, typically 30 feet or more below the water table. By pumping water from the bottom of this well, a cone-shaped depression, commonly referred to as a cone of depression, is created on the water table with the well as the apex. The lighter weight floating hydrocarbon liquid then collects in the well where it is removed by a second pump which is located near the liquid surface in the well. Systems such as this are disclosed in Finch U.S. Pat. No. 3,901,811 and in Solomon U.S. Pat. No. 4,273,650. These patented systems deal with fixed position pumps which may be rendered ineffective in situations where the water table is not static such that the respective fluid interfaces, hydrocarbon/water and hydrocarbon/air, can be maintained in the necessary relationship to each other for the systems to operate properly.
In an attempt to deal with this kind of problem, floating pump systems have been devised. These systems rely on various kinds of skimmers to remove the thin layer of hydrocarbons floating on the water in the well. Systems of this type are disclosed in U.S. Pat. No. 4,469,170 of Farmer, Jr., U.S. Pat. Nos. 4,663,037 and 4,761,225 of Breslin, U.S. Pat. Nos. 4,404,093 and 4,746,423 of Moyer and U.S. Pat. No. 4,527,633 of McLaughlin et al.
While the skimmer systems of these prior patents would be effective under particular conditions establishing the parameters for which they have been particularly designed, the devices of this type are frequently very inefficient and often require the transfer of large volumes of water with very small volumes of the contaminating liquid hydrocarbon product.
We have developed an improved system which somewhat resembles a floating well skimmer but differs therefrom in that it captures the volume of the floating product and transfers it into a controlled reservoir, from which it is positively pumped for removal.